1. Field of the Invention
This invention relates to a filter element for a transcatheter embolic protection device.
2. Description of the Related Art
The invention is particularly concerned with filter elements for transcatheter embolic protection devices of the type described in our WO-A-9923976. One type of such embolic filter essentially comprises a filter body mounted on an associated collapsible support frame which can be collapsed by means of a catheter for deployment of the filter through a patient's vascular system. Upon retraction of the catheter the support frame and filter body expand outwardly from across a blood vessel within which the filter is positioned to filter blood flowing through the blood vessel.
The support structure is generally of superelastic or shaped memory material such as Nitinol™ which provides the circumferential pressure on expansion to secure the filter body in a close fit within the vessel.
It is important to achieve apposition of a filter body with the wall of the vessel in which the filter is deployed to ensure that there is no pathway between the filter body and the vessel wall through which embolic material could pass. This is not a simple issue in view of the wide variations in vessel geometry and the variable physical properties of a vessel lining at different locations even within a single vasculature.
When the filter element is being pulled through a small diameter conduit or opening for loading and retrieval, there are certain forces exerted on the support frame. The first is on entry of the proximal end into the tube and when the whole of the proximal end has been inserted into the tube and the distal end is about to be inserted into the catheter tube. Considerable loading forces are generated which in some cases require considerable retraction forces to overcome.
There is therefore a need to provide a support frame for a filter which will address these problems.